To prevent unauthorized duplication or alteration of documents, frequently there is special indicia or a background pattern that may be provided for sheet materials such as tickets, checks, currency, and the like. The indicia or background pattern is imposed upon the sheet material usually by some type of printing process such as offset printing, lithography, letterpress or other like mechanical systems, by a variety of photographic methods, by xeroprinting, and a host of other methods. The pattern or indicia may be produced with ordinary inks, from special inks which may be magnetic, fluorescent, or the like, from powders which may be baked on, from light sensitive materials such as silver salts or azo dyes, and the like. Most of these patterns placed on sheet materials depend upon complexity and resolution to avoid ready duplication. Consequently, they add an increment of cost to the sheet material without being fully effective in many instances in providing the desired protection from unauthorized duplication or alteration.
Various methods of counterfeit-deterrent strategies have been suggested including Moire-inducing line structures, variable-sized dot patterns, latent images, see-throughs, bar-codes, and diffraction based holograms. However, none of these methods employs a true scrambled image or the added security benefits deriving therefrom.
The inventor of the technology disclosed in this patent previously invented a system for coding and decoding indicia placed on printed matter by producing a parallax panoramagram image. These principles and embodiments of U.S. Pat. No. 3,937,565, issued Feb. 10, 1976 and are hereby incorporated by reference. The indicia were preferably produced photographically using a lenticular plastic screen (i.e. a lenticular screen) with a known spatial lens density (e.g. 69 lines per inch). A specialized auto-stereoscopic camera might be used to produce the parallax image such as the one described in this inventor's U.S. Pat. No. 3,524,395, issued Aug. 18, 1970, and U.S. Pat. No. 3,769,890, issued Nov. 6, 1973.
Photographic, or analog, production of coded indicia images has the drawback of requiring a specialized camera. Also, the analog images are limited in their versatility in that an area of scrambled indicia is generally noticeable when surrounded by non-scrambled images. Also, it is difficult to combine several latent images, with potentially different scrambling parameters, due to the inability to effectively re-expose film segments in generating the scrambled, photographic image. Furthermore, it is difficult to produce secure documents, such as currency, traveler's checks, stock and bond certificates, bank notes, food stamps and the like which are formed from a durable material resistant to tearing, staining, fraying, and deterioration from day-to-day contact.
Accordingly, a method and apparatus are needed whereby the photographic process and its results are essentially simulated digitally via a computer system and related software. Additionally, a system is needed whereby scrambled latent images can be integrated into a source image, or individual color components thereof, so that the source image is visible to the unaided eye and the latent image is visible only upon decoding. Also needed is the ability to incorporate multiple latent images, representing different “phases”, into the source image for added security. Furthermore, what is needed is the ability to apply this technology to a durable substrate, such as a synthetic paper, and to incorporate an appropriate verification lens integral within the document's structure.